Various materials are used to construct architectural doors. Architectural wood doors are well known. Wood doors, however, when exposed to rain, snow, sun and other elements require frequent maintenance including the application of various stains and clear coats. Wood doors can also warp and are subject to rot. There is a need for a door having low maintenance that is not susceptible to the elements. Various alternatives to wood are available.
Doors having steel facing panels are common. These steel panel doors are fairly inexpensive to construct and are somewhat dimensionally stable under temperature fluctuations. The initial start up costs associated with producing a steel door is high. High pressure tools are required to form the panels. However, unless the steel panels used have a high thickness, doors constructed with steel panels are subject to denting. In addition, imparting a crisp multi-directional wood grain appearance to a steel panel door is typically not done.
Doors constructed with fiberglass facing panels are also common. Fiberglass facing panels have significant benefits over steel. Fiberglass facing panels can be constructed to resemble a panelized wooden door. However, fiberglass doors are very expensive to construct. Like steel doors, the start-up costs associated with production are high and production rates are very slow. Expensive molds must be used to produce the panels having a panelized wooden door appearance. The raw materials for fiberglass doors are also relatively expensive. Fiberglass doors also have problems with dimensional stability resulting from temperature fluctuations. Such dimensional stability can eventually damage a door.
Doors constructed with PVC facing panels are also well known. PVC facing panels are less expensive to produce than the fiberglass panels as manufacturing costs and raw material costs are both less than that of fiberglass panels. However, PVC, like fiberglass, is dimensionally unstable in response to temperature fluctuations. PVC softens considerably at 180° F. As a result, PVC is inappropriate for use in storm doors and doors that are used in combination with storm doors where it is possible to obtain temperatures in excess of 180° F. in the space between the storm door and the door in response to exposure to direct sunlight. For example, the space between a dark painted door and a full view storm door (i.e., large window) can reach up to 230° F. and 240° F. Consequently many materials undergo considerable deterioration when used on an exterior door used in association with a storm door or used as a storm door.
For the foregoing reasons there is a need for a door constructed with opposing door panels that are manufactured using inexpensive manufacturing techniques and inexpensive raw materials. There is a further need for doors constructed with door panels that are resistant to denting and are dimensionally stable under temperature fluctuations.
Others have tried to use produce composite materials. These materials, however, are not suitable for use in the formation of composite door skins from both manufacturing and product lifetime perspectives.
U.S. Pat. Nos. 5,486,553 and 5,539,027, both entitled “Advanced Polymer/Wood Composite Structural Member” to Deaner et al. disclose the formation of structural members from a polymer and wood composite. The structural members are formed from a composite containing 30 to 50 wt-% of sawdust along with 50 to 70 wt-% of a polyvinyl chloride polymer. The composite is first blended and then extruded into pellets. The pellets are then extruded into the desired structural member. The disclosed composite, however, is not suitable for use in the formation of doors because the material may degrade when exposed to high temperatures. Furthermore, the use of the disclosed composite requires additional manufacturing steps. Furthermore, the composite must first be pelletized before formation into the final shape as a structural member. Finally, the final product does not have the appearance of wood.
U.S. Pat. No. 5,700,555, entitled “Sandable and Stainable Plastic/Wood Composite” to Grill discloses a composite article that may be used to form components of steel, fiberglass or wood door. The article includes a first zone made entirely of plastic and a second zone made of plastic and natural fiber. The first and second zones are integral and are continuously coextruded. The ratio of natural fiber in the second zone is between 10% and 55%. The outer surface of the second zone includes embossing to resemble wood grain. The outer surface has sufficient porosity so as to hold and retain wood stain and paint so that the composite article is stainable to resemble genuine wood. The composition of the second zone may include between 45% and 90% polyvinylchloride, between 10% and 55% natural fiber, and external lubricate and a fusion enhancer.
U.S. Pat. Nos. 5,827,607, 5,932,334, and 6,015,611, each entitled “Advanced Polymer Wood Composite” to Deaner et al. and U.S. Pat. No. 6,015,612, entitled “Polymer Wood Composite” to Deaner et al. disclose the formation of structural members from a polymer and wood composite. The structural members are formed from a composite containing 30 to 50 wt-% of sawdust along with 40 to 70 wt-% of a polymer containing vinyl chloride and less than 8 wt-% of water. Like the other Deaner et al. references discussed above, the composite is first blended and then extruded into pellets. The pellets are then extruded into the desired structural member, which requires additional manufacturing steps.
U.S. Pat. No. 5,866,264, entitled “Renewable Surface For Extruded Synthetic Wood Material” to Zehner et al discloses a cellulosic fibrous polymer composite material having a renewable surface that is coextruded therewith.
U.S. Pat. No. 5,869,138, entitled “Method For Forming Pattern On A Synthetic Wood Board” to Nishibori discloses a method of forming a wood grain pattern on a synthetic wood board. Nishibori discloses a multi-step process for forming a wood grain. The synthetic wood board is first subject to a first grinding process along its entire surface of at least one side. A colorant is then coated on the ground surface. The colorant impregnates in wood meal on the surface. The surface is then subject to a second grinding process and abraded to form woody like appearance. The board is then subject to a grain printing process.